Vitreoretinal surgeries are conducted in an operating room under sterile conditions to prevent the risk of infection, particularly endophthalmitis; a rapid devastating infection that can cause blindness in a few days. The patient's eye is cleaned with an antiseptic, and then isolated with a sterile drape that fully covers the patient with only the eye exposed. A sterile field is established around the patient such that any personnel or instrumentation must be suitably scrubbed, draped or sterilized following standard aseptic procedures. A surgical microscope is used to view the interior of the eye through the patient's cornea and lens. The surgeon uses sterilized instruments including an infusion cannula to maintain intraocular pressure; an entry system to enable access to the posterior segment of the eye; a vitrectomy probe to cut and aspirate the vitreous gel; an illumination probe to provide light for visibility; various micro forceps and scissors for membrane manipulation and dissection; and specialized instruments as needed. Conventionally, the infusion, vitrectomy probe, illumination probe and aspiration are driven by a surgical console that sits outside the sterile field, and controlled by the surgeon using a multifunction foot pedal. Changes to the console settings are conducted by either a sterile scrub nurse assistant or circulating nurse that is outside of the sterile field.
Following a vitrectomy to repair a retinal tear and/or detachment, the surgeon may leave a tamponade in the eye to stabilize the retina during the healing process. If the detachment is localized and not severe, the tamponade can be a gas bubble of air or a mixture of air with an expansile gas (SF6, C2F6, or C3F8). The bubble is absorbed over time from days or weeks depending on the gas and concentration used and no further surgery is required. For severe or chronic detachments, however, silicone oil is used and typically left in the eye for 3 to 12 months to allow the retina to reattach. Follow-on surgery is required to remove the oil. Typical oils are highly purified silicone (polydimethylsiloxane) in the viscosity range of 1000 to 5000 centistokes that are injected to fill the eye at the conclusion of vitreous surgery. The fluid volume required is typically 4-6 milliliters and can approach 10 milliliters or more in patients that are highly myopic (long eyes).
Due to the high viscosity of the fluid and the relatively small size of the incisions used for vitrectomy surgery, the injection of the silicone is performed using a pressurized syringe as it is difficult to manually generate the forces required to inject the viscous silicone oil through the small incision. Conventional methods are to use devices, such as those described U.S. Pat. No. 7,601,140 or U.S. Pat. No. 6,997,904, to attach to a syringe full of silicone oil to a high-pressure air source controlled by the surgical console. The surgeon modulates the silicone oil flow rate through the use of a foot pedal up to the maximum pressure setting on the console, which is typically supplied with hospital wall air or large nitrogen bottles. The surgeon will use the maximum pressure at the beginning of the fill cycle to induce the maximum flow rate to reduce the time it takes to fill the eye. As the eye fills, he will decrease the pressure so that he can reduce the flow rate to prevent overfilling and thus over pressurizing the eye. The ability to continuously modulate the flow rate is essential to the procedure.
Some of the difficulties with conventional methods for delivery of silicone oil arise from performing an injection within a sterile operating field using a device that is coupled to a required console located outside of the non-sterile field. As a result, two nurses are typically required to assist the surgeon with setting up or operating the device. A sterile scrub nurse connects the syringe filled with silicone oil to the pressure delivery device and carefully passes the tube set to a non-sterile circulating nurse ensuring that the sterile barrier is not compromised. The non-sterile circulating nurse connects the pressure delivery device tube set to the console and adjusts the maximum pressure settings. In addition to requiring multiple personnel, the requirement of having an additional connection (or connections) that must pass from the sterile field to outside of the sterile field is also undesirable. Also, the console devices used for providing pressure for the pressure delivery device are typically limited to providing a pressure available from a “house” gas source. This pressure limitation with the inherent pressure drop of the console pneumatic system, results in a maximum output pressure of only about 80 psig or less. As improvements in vitreous surgical instruments allow surgeries to move from the traditional 20 gauge to smaller 23, 25 and 27 gauge incisions, the limitation of having 80 psig (or less) pressure available means that longer injection times are required for such smaller incisions. These conventional methods for delivery of silicone oil are still in use today, in spite of decades of awareness of the difficulties and shortcomings associated with the conventional methods. Thus, there is a long-felt need within the art to provide an alternative to such conventional methods.
U.S. Pat. No. 8,002,753 describes a self-contained pressurized injection device. The device includes a volume of pressurized fluid, where the volume can be moved between a first position and a second position. In the second position, the pressurized fluid becomes available for providing pressure for pushing a medicament out of the injection device. The flow rate of a medicament out of the injection device can be controlled by constricting the size of the conduit for delivering the medicament.